An evaluation of superplasticity in aluminum-scandium alloys processed by equal-channel angular pressing

An Al-0.2%Sc alloy and an Al-3%Mg-0.2%Sc alloy were subjected to equal-channel angular pressing to a strain of ∼8 to produce grain sizes of ∼0.7 and ∼0.2 μm, respectively. Because of the presence of some areas of subgrain boundaries in the Al-3%Mg-0.2%Sc alloy, additional samples of this alloy were subjected to ECA pressing to a strain of ∼12. In both alloys, the grain sizes were reasonably stable up to annealing temperatures above 700 K. Tensile specimens were machined from the as-pressed samples for testing at elevated temperatures. The Al-3%Mg-0.2%Sc alloy pressed to a strain of ∼12 exhibited exceptional ductility with elongations up to a maximum of ∼1560% at 673 K at the high strain rate of 3.3 × 10^-2 s^-1. By contrast, the Al-0.2%Sc alloy failed under all conditions at elongations <400%. The difference in behavior between these two alloys is attributed to the nature of the deformation mechanism which serves to accommodate the superplastic process.